This invention relates to electrostatic position sensors and more particularly to brushless angle resolvers incorporating reflected electrostatic field detection concepts.
A number of prior art angle resolvers utilize electrostatic technology to produce an output signal indicative of angular position. A variety of sensors have been developed which include AC as well as DC excitation. The electrostatic angle resolver is essentially comprised of two variably shaped metallic plates the first being stationary and the second rotated in opposition to the first to vary the plate surface area exposed between the two plates thereby creating a variable capacitor. An electrostatic charge source is connected to the stationary plate and the electrostatic charge acquired by the moving plate from the stationary plate is reflected back to the stationary plate by way of a coupling capacitor. After reflection to the stationary plate, the signal is electronically analyzed and the position of the rotating plate with respect to the stationary plate is ascertained. Examples of such devices are shown in U.S. Pat. No. 4,092,579 to Weit, U.S. Pat. No. 4,040,041 to Fletcher et al., U.S. Pat. No. 4,435,702 to Imai, U.S. Pat. No. 3,961,318 to Farrand, U.S. Pat. No. 4,418,348 to Tanaka et al., and U.S. Pat. No. 4,238,781 to Vercellotti et al.
Typically, the output signal of an angle resolver of the prior art is coupled from the rotor to the stator by means of a coupling capacitor. The coupling capacitor is formed by parallel plates that are aligned and registered on the stator and rotor elements of the device usually taking the form of opposing disk shaped electrodes. An inherent problem with sensors of the prior art is the loss of signal strength due to stray capacitances affecting the rotor and stator coupling capacitor electrode plates. When an electrostatic angle resolver application calls for installation in close proximity to nearby metallic objects, the problems attributable to stray capacitances become more significant. Additionally, where size or space constraints placed upon the angle resolver due to a particular application limit the available space for the device, additional problems may arise.
An angle resolver design which eliminates the rotor to stator coupling capacitor would result in a space claim savings of up to 50% of the original volume of the resolver in most applications.